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DIY: Do It Yourself Post here to share or improve your wrench turning skills! All BMW E46 DIY tips, tales, and projects discussed inside. Learn to work on your car and know the right BMW parts you will need!

In order to do this job, you have to take off the reinforcement plate (mine had one), then it is easier to access these sensors as well as to route the wiring. Dropping the exhaust is not necessary in contrasts to what the TIS says as this is proof.

Bank 1 has this stupid dummy bracket, observe in sdbimmer's diagram in above posts. You can see it in my first few pictures. I used a dremmel bit made for metal and sawed off this sucker because it was preventing me from getting my socket and extension in. A word of caution that when you cut this thing off, sparks will fly. Also let your dremmel or alike rest after trying to cut. If you don't you can burn out the motor. Ask me how I know.

You'll also see that I painted it. I mainly painted it so that the rust would not eat through the pipe. Granted that there is already rust on the surface, but overtime, I think a freshly cut metal may accelerate the rust, so I used high temp paint. High temp primer first then the paint, two coats each.

The 4th picture, has the tool setup on how to remove the bank1 sensor, note in the picture that you have to saw off the bracket first. Third and sixth picture show how I used a small adjustable that was thin enough and could open wide enough to slip between the pipes. From there I used a three pound sledge and gave it a wack to loosen the seize. Be sure to wack the correct way otherwise your tightening it. Just look at the threads on a new o2 sensor to see which way one should wack it.

7th and 8th picture shows the routing of the wiring. Once you remove the reinforcement plate or equivalent, you can easily maneuver the wiring to their mounts. I would drop the new sensors in from the top. I tied additional strings to them in order to get them down. Be sure to route in the same manner as the originals, so take lots of pictures.

The last shows one of the post cat o2's with over 97k on it. I did not have any issues as far as why I replaced it but simply for the fact that these typically only last 100k and I did them as part of an overhaul with sensors and just general maintenance. I replaced my pre-cats too along with a boat load of other stuff.

After 8 or 9 months of overhaul, I was finally able to enjoy getting her back on the road. Initially lots of DTCs were stored once I plugged the battery back in. No SES light. I just cleared the codes and after 350 miles so far this week, no codes, no problems, no leaks, and no issues.

I am getting a P0420 code with my 323I. It just started. The car has about 150K on it none of the 02's have been replaced. Do I need to replace the bank 1 Pre or post Cad O2? Should I just replace all 4 while I am at it?

Bump this up
I'm getting code p0135
Bank 1 sensor 1 wich sensor is that 1? Image pls?
And wer can I purchased the sensor for low price?..

What you require is the pre-cat O2 sensor. The OE BMW sensor will cost close to $200.00 each. You can buy the OEM version which is identical (made by Bosch), other than the BMW stamp. I recently purchased them for $65.00 a piece online. Serach the fourm sponsors or online. Very easy DIY. You will need a special O2 socket wrench. AutoZone will lend you all necessary tools.

When purchasing the O2 sensors, the two pre-cats are the same part for each sensor. The post-cats are a different part number and have a longer cable connection due to the routing down to the bottom.

My BMW dealer said it would cost $325 to replace the post catalytic O2 sensor on my 2001 325i.He also reprogramed and encoded the DME saying that might be the problem instead. Bulletin 12 07 04 130,000 miles. Still probably should be changed

I had SES light on with 165k and replaced all three 02 sensors with botsh and light is gone. I was not able to chanege the 2nd pre cat and I gave up becouse the space is really tight there almost impossible to apply force and I do not want to cut the brackets to remove it.
So my question is it ok to leave this sucker on as it not giving any codes?

Thank for replay and video you are doing really good job for BMW peaple. but my mistake. I have hard time with post cat not the pre cat the one on the top.
Pre cats wore really easy after watching your video on YouTube.

2 Pre-cat located and easily accesible on the passenger side of the engine
2 Post-cat located underneath the car and are a real pain to get to (Well as least one of them)

If you have a O2 sensor problem most likely it would be the Pre-cats and I would change those out first. The Post-cats mainly deal with exhaust emissions so I wouldn't go replacing those unless one was faulty, or you failed emissions do to an O2 sensor problem.

But before you dive into this either get yourself a code reader or go to a shop to get the code read for free to determine if it is O2 related or not. For these sensors are a bit expensive I paid $90 each Pre-Cat and about $120 for each Post-cat.

So make sure you know the problem is before you just go dropping money on stuff like this.